Information AboutVirtual Lan |
| CATEGORIES ABOUT VIRTUAL LAN | |
| local area networks | |
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A VLAN consists of a network of computers that behave as if connected to the same link layer network - even though they may actually be physically connected to different Segments of a LAN. Network administrators configure VLANs through software rather than hardware, which makes them extremely flexible. One of the biggest advantages of VLANs emerges when physically moving a computer to another location: it can stay on the same VLAN without the need for any hardware reconfiguration. ADVANTAGES
PROTOCOLS AND DESIGN The primary protocol currently used in configuring virtual LANs is IEEE 802.1Q , which describes how traffic on a single physical network can be partitioned into virtual LANs by tagging each frame or packet with extra bytes to denote which virtual network the packet belongs to. Prior to the introduction of the 802.1Q standard, several proprietary protocols existed, such as Cisco 's ISL (Inter-Switch Link, a variant of IEEE 802.10 ) and 3Com 's VLT ( Virtual LAN Trunk ). ISL is no longer supported by Cisco. Early network designers often configured VLANs with the aim of reducing the size of the Collision Domain in a large single Ethernet segment and thus improving performance. When Ethernet Switch es made this a non-issue (because they have no collision domain), attention turned to reducing the size of the Broadcast Domain at the MAC Layer . Virtual networks can also serve to restrict access to network resources without regard to physical topology of the network, although the strength of this method remains debatable as VLAN Hopping is a common means of bypassing such security measures. Virtual LANs operate at Layer 2 (the Data Link Layer ) of the OSI Model . However, administrators often configure a VLAN to map directly to an IP network, or Subnet , which gives the appearance of involving Layer 3 (the Network Layer ). In the context of VLANs, the term "trunk" denotes a network link carrying multiple VLANs, which are identified by labels (or "tags") inserted into their packets. Such trunks must run between "tagged ports" of VLAN-aware devices, so they are often switch-to-switch or switch-to-). A Router (Layer 3 device) serves as the Backbone for network traffic going across different VLANs. On Cisco devices, VTP (VLAN Trunking Protocol) allows for VLAN Domains , which can aid in administrative tasks. VTP also allows "pruning", which involves directing specific VLAN traffic only to switches which have ports on the target VLAN. ASSIGNING VLAN MEMBERSHIPS The four methods of assigning VLAN memberships that are in use are:
Port-based VLANs A port based VLAN switch determines the membership of a data frame by examining the configuration of the port that received the transmission or reading a portion of the data frame’s tag header. A four-byte field in the header is used to identify the VLAN. This VLAN identification indicates what VLAN the frame belongs to. If the frame has no tag header, the switch checks the VLAN setting of the port that received the frame. SEE ALSO
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